Data carrier provided with at least two decoding stages

ABSTRACT

In a data carrier ( 1 ) which includes receiving means ( 5 ) for receiving a modulated carrier signal (MTS) which contains a data signal (DS 1 ) encoded in conformity with an encoding method (MA, PW, MI, RTZ, FSK, PSK), demodulation means ( 9 ) for demodulating the received modulated carrier signal (MTS) and for outputting the encoded data signal (DS 1 ) contained therein, decoding means ( 10, 20 ) for decoding the encoded data signal (DS 1 ) and for outputting data (D 1,  D 2 ), and data processing means ( 11 ) for processing the data (D 1,  D 2 ) output by the decoding means ( 10, 20 ), the decoding means ( 10, 20 ) are provided with at least a first decoding stage ( 12 ) and a second decoding stage ( 13 ), the first decoding stage ( 12 ) being arranged to decode a data signal (DS 1 ) encoded in conformity with a first method (RTZ) whereas the second decoding stage ( 13 ) is arranged to decode a data signal (DS 1 ) encoded in conformity with a second method (MI).

The invention relates to a data carrier which includes receiving meansfor receiving a modulated carrier signal which contains a data signalencoded in conformity with an encoding method, demodulation means fordemodulating the received modulated carrier signal and for outputtingthe encoded data signal contained therein, decoding means for decodingthe encoded data signal and for outputting data, and data processingmeans for processing the data output by the decoding means.

A data carrier of the kind set forth in the first paragraph is knownfrom the document EP 0 669 591 A2 and is formed by a so-calledtransponder.

Data to be transmitted to the data carrier can be encoded in conformitywith a pulse width encoding method by a transmitter station so as toform an encoded data signal and a carrier signal can be modulated withthe encoded data signal by amplitude modulation. According to the pulsewidth encoding method, a data bit “0” of the data to be transmitted isencoded with a smaller number of carrier signal oscillations and a databit “1” of the data to be transmitted is encoded with a larger number ofcarrier signal oscillations. The carrier signal oscillations of eachdata bit are separated from one another by a respective blankinginterval in the encoded data signal.

The known data carrier includes receiving means which are formed by anantenna coil. A modulated carrier signal output by the transmitterstation can be received by the receiving means.

The data carrier also includes demodulation means for demodulating thereceived, modulated carrier signal by amplitude demodulation and foroutputting the encoded data signal contained in the modulated carriersignal.

By counting the carrier signal oscillations present between two blankingintervals in the encoded data signal, the decoding means of the knowndata carrier determine whether a data bit “0” or a data bit “1” ispresent in the encoded data signal; the decoding means thus decode theencoded signal. Data bits determined by the decoding means are output asreceived data to processing means of the data carrier for the furtherprocessing of the received data. The processing means are formed by acontrol unit, a digital comparator and a memory.

The known data carrier has been found to have the drawback that the datacarrier is capable of decoding exclusively received encoded data signalswhich have been encoded in conformity with the pulse width encodingmethod. Consequently, data contained in received encoded data signalsand encoded in conformity with a different encoding method in atransmitter station cannot be decoded by the decoding means of the knowndata carrier; therefore, such data cannot be processed by the datacarrier.

Furthermore, a special drawback is encountered in that the decodingmeans of the known data carrier are constructed in such a manner thatthey decode every received encoded data signal in conformity with thepulse width coding method and hence output false data when a receivedencoded data signal has been encoded according to an encoding methodother than the pulse width encoding method. Such false data could inducevery faulty operation of the known data carrier; for example, the doorsto a security zone could then be opened to a person who is notauthorized to enter such a zone.

It is an object of the invention to eliminate the described problems andto provide an improved data carrier of the kind set forth in the firstparagraph. In a data carrier of the kind set forth in the firstparagraph this object is achieved according to the invention in that thedecoding means include at least a first decoding stage and a seconddecoding stage, the first decoding stage being arranged to decode a datasignal encoded in conformity with a first encoding method whereas thesecond decoding stage is arranged to decode a data signal encoded inconformity with a second encoding method.

This offers the advantage that the data carrier is arranged to decodedata which is contained in a received encoded data signal and has beenencoded in conformity with the first or the second encoding method.Known encoding methods are, for example, a Manchester encoding method, apulse width encoding method, a Miller encoding method, a return-to-zeroencoding method, a frequency shift keying or FSK encoding method, or aphase shift keying or PSK encoding method.

A special advantage is then achieved in that a data carrier is thussuitable for use in various fields of application, for example foraccess control systems or toll systems in which different encodingmethods may be customary or even standardized. In this context,reference is made, for example to a known “Approximity Standard” (ISO 14443); according to this standard a Miller encoding method is used forcommunication with a data carrier of the type A whereas in the case ofcommunication with a data carrier of the type B a No-Return-To-Zeroencoding method is used.

It has been found that the steps disclosed in Claim 2 are advantageouslytaken in a data carrier as disclosed in Claim 1. This offers theadvantage that a decision stage of the data carrier decides which of thedata output by the at least two decoding stages is to be used forfurther processing by means of the processing means. It is thus avoidedthat a data signal encoded by a transmitter station in conformity with afirst encoding method is decoded in conformity with a second encodingmethod in one of the decoding stages of the data carrier and that falsedata output by this decoding stage are processed in the processingmeans.

It has been found that it is advantageous to take the steps described inClaim 3 in a data carrier device as disclosed in Claim 2. This offersthe advantage that the decision stage can decide which of the dataoutput by a decoding stage exhibits the lowest error rate, for exampleon the basis of error rate information of the data output by thedecoding stages, which error rate information can be determined in thedecoding stages, from redundancy information contained in the encodeddata signal and constitutes decision supporting information. Thedecoding stage outputting the data having the lowest error rate thenconstitutes the decoding stage which is suitable for decoding thereceived encoded data signal.

It has been found that it is advantageous to take the steps disclosed inClaim 4 in a data carrier device as disclosed in Claim 2. This offersthe advantage that a transmitter station can supply the data carrierwith decoding stage instruction information which is contained in themodulated carrier signal and is capable of characterizing the decodingstage of the data carrier which is arranged to decode an encoded datasignal transmitted by the transmitter station in the modulated carriersignal after the decoding stage instruction information. A transmitterstation communicating with the data carrier can thus always specify therespective decoding stage suitable for the decoding of the encoded datasignal contained in the modulated carrier signal transmitted by thetransmitter station.

It has been found that it is advantageous to take the steps of Claim 5in a data carrier device as disclosed in Claim 1. The advantage is thusachieved that data received by the data carrier before the reception ofa decision as to which decoding stage is suitable for the decoding of areceived encoded data signal will not be lost.

The steps disclosed in Claim 6 are advantageously taken in a datacarrier device as disclosed in Claim 2. At the beginning of eachcommunication operation with a transmitter station for which it is notyet known which encoding method is used therein so as to encode the datato be transmitted, the decision stage then applies the data of the firstdecoding stage to the processing means which decode a received encodeddata signal in conformity with an encoding method preferably used bytransmitter stations. In the case of data carriers without storage stagethis offers the advantage that most of the data received in the datacarrier before a decision as to which decoding stage is suitable for thedecoding of a received encoded data signal will not be lost.

It has been found that the steps disclosed in Claim 7 are advantageouslytaken in a data carrier device as described in Claim 1. This offers theadvantage that the data carrier is also arranged to transmit an encodeddata signal which is contained in a modulated carrier signal andcontains data which has been encoded in conformity with one of at leasttwo different encoding methods.

The invention will be described in detail hereinafter on the basis oftwo embodiments which are shown in the drawings, however, without theinvention being restricted thereto.

FIG. 1 shows a block diagram of a first embodiment of a smart cardaccording to the invention which is arranged for the contactlessexchange of data with a base station, the smart card including twodecoding stages for the decoding of received data signals encoded inconformity with a Return-To-Zero encoding method or a Miller encodingmethod.

FIG. 2 shows a waveform of a data signal which has been encoded inconformity with a Manchester encoding method and may be contained in amodulated carrier signal received by the smart card.

FIG. 3 shows a waveform of a data signal which has been encoded inconformity with a pulse width encoding method and may be contained in amodulated carrier signal received by the smart card.

FIG. 4 shows a waveform of a data signal which has been encoded inconformity with the Miller encoding method and may be contained in amodulated carrier signal received by the smart card.

FIG. 5 shows a waveform of a data signal encoded in conformity with theReturn-To-Zero encoding method and may be contained in a modulatedcarrier signal received by the smart card.

FIG. 6 shows a waveform of a data signal which has been encoded inconformity with a frequency keying encoding method and may be containedin a modulated carrier signal received by the smart card.

FIG. 7 shows a waveform of a data signal which has been encoded inconformity with a phase keying encoding method and may be contained in amodulated carrier signal received by the smart card.

FIG. 8 shows a waveform of a modulated carrier signal which can bereceived by the smart card and contains a data signal encoded inconformity with the Return-To-Zero encoding method.

FIG. 9 shows a waveform of the encoded data signal which is contained inthe modulated carrier signal shown in FIG. 8 and is applied to the twodecoding stages of the smart card, said decoding stages outputting inresponse thereto first and second data as shown in FIG. 9.

FIG. 10 shows a block diagram of a second embodiment of a smart cardaccording to the invention which is arranged for the contactlessexchange of data with a base station, an encoded data signal received bythe smart card in a modulated carrier signal being buffered in a storagestage prior to decoding by means of the two decoding stages.

FIG. 1 shows a block diagram of a smart card 1 which constitutes a firstembodiment of a data carrier according to the invention and is arrangedfor the contactless exchange of data with a base station 2. The basestation 2 constitutes a ticket machine which is to debit an amount of 9Euros to the balance due to the user of the smart card 1 which is storedas balance data in the smart card 1. To this end, the base station 2includes data processing means 3 in which debit data AD representing theamount of 9 euros is stored as a bit sequence “1001”.

The data processing means 3 are also arranged to generate redundancyinformation RD on the basis of which the smart card 1 can recognizeerrors in the received debit data AD which have occurred during thetransmission of the debit data AD from the base station 2 to the smartcard 1. The data processing means 3 are arranged to generate theredundancy information RD by determining a sum of the bit sequence“1001” of the debit data AD. Redundancy data RD is then determined asredundancy information which has the value “2” for the bit sequence“1001” of the debit data AD and corresponds to the bit sequence “10”.

Transmission data ÜD to be applied to the smart card 1 is formed by thedata processing means 3 by chaining the bit sequences of the debit dataAD and the redundancy data RD. The transmission data ÜD is formed by thebit sequence “100110” in the case of a bit sequence “1001” of the debitdata AD and a data sequence “10” of the redundancy data RD. Thedescribed determination of transmission data ÜD is customarily performedin known smart cards; debit data AD may then be formed, for example by abit sequence of 64 bits whereas redundancy data RD is formed by a bitsequence of 16 bits.

The FIGS. 2, 3, 4, 5, 6 and 7 show waveforms of encoded data signals DS1in which the bit sequence “100110” of the transmission data ÜD has beenencoded in conformity with six different known encoding methods. Inorder to obtain the waveform of the encoded data signal DS1(MA) shown inFIG. 2, a Manchester encoding method was applied; in order to obtain thesignal waveform of the encoded data signal DS1(PW) shown in FIG. 3, apulse width encoding method was applied; in order to obtain the signalwaveform of the encoded data signal DS1(MI) shown in FIG. 4, a Millerencoding method was applied; in order to obtain the signal waveform ofthe encoded data signal DS1(RTZ) shown in FIG. 5, a Return-To-Zeroencoding method was applied; in order to obtain the waveform of theencoded data signal DS1(FSK) shown in FIG. 6, a frequency shift keying(FSK) encoding method was applied, and in order to obtain the waveformof the encoded data signal DS1(PSK) shown in FIG. 7, a phase shiftkeying (PSK) encoding method was applied. A number of appropriatefurther encoding methods will be known to those skilled in the art.

The data processing means 3 of the base station 2 also include encodingmeans for the encoding of bit sequences of transmission data ÜD, forexample the bit sequence “100110”, in conformity with the Return-To-Zeroencoding method. The encoding means of the data processing means 3 arecapable of delivering the waveform of the encoded data signal DS1(RTZ)with the bit sequence “100110” as shown in FIG. 5.

The data processing means 3 of the base station 2 also includemodulation means for modulating an encoded data signal DS1(RTZ), outputby the encoding means of the data processing means 3, by amplitudemodulation. A carrier signal TS which has a carrier frequency of 13.56MHz and a period duration T(TS) is then modulated with an encoded datasignal DS1(RTZ) output by the encoding means, the modulation depth beingfixed at 100%.

FIG. 8 shows a modulated carrier signal MTS which can be output by themodulation means and is formed, by the carrier signal TS during timeintervals TA in which the encoded data signal DS1(RTZ) contained in themodulated carrier signal MTS has a high amplitude value. During furthertime intervals TB, in which the encoded data signal DS1(RTZ) containedin the modulated carrier signal MTS has a low amplitude value, nocarrier oscillations of the carrier signal TS are contained in themodulated carrier signal MTS.

The base station 2 also includes transmission and receiving means 4whereto a modulated carrier signal MTS produced by the data processingmeans 3 can be applied. The transmission and receiving means 4 arearranged to transmit a modulated carrier signal MTS, applied thereto bythe data processing means 3, in an electromagnetic alternating field.The transmission and receiving means 4 are also arranged to receive amodulated carrier signal MTS which is contained in an electromagneticalternating field and to output a received modulated carrier signal MTSto the data processing means 4 for the further processing of datacontained in the modulated carrier signal MTS.

The smart card 1 includes transmission and receiving means 5 which arearranged to transmit a modulated carrier signal MTS in a transmissionmode of the smart card 1 and to receive a modulated carrier signal MTSin a receiving mode of the smart card 1, said modulated carrier signalMTS containing a data signal DS1 encoded in conformity with an encodingmethod. A modulated carrier signal MTS received by the transmission andreceiving means 5 can be output via a terminal 6 of the transmission andreceiving means 5.

A power supply stage 7 of the smart card 1 is connected to the terminal6 of the transmission and receiving means 5. The power supply stage 7can receive a received modulated carrier signal MTS. The power supplystage 7 is arranged to generate an operating voltage by rectifying amodulated carrier signal MTS applied thereto. An operating voltagegenerated by the power supply stage 7 can be applied (in a manner notshown in FIG. 1) to further stages of the smart card 1.

A clock extraction stage 8 of the smart card 1 is also connected to theterminal 6 of the transmission and receiving means 5. The clockextraction stage 8 can be supplied with a received modulated carriersignal MTS. The clock extraction stage 8 is arranged to extract theclock of a received modulated carrier signal TS and to output anextracted carrier signal TS.

The smart card 1 includes demodulation means 9 for demodulating areceived modulated carrier signal MTS and for outputting an encoded datasignal DS1 contained in the modulated carrier signal MTS. Thedemodulation means 9 are connected to the terminal 6 of the transmissionand receiving means 5 and are arranged to demodulate a receivedmodulated carrier signal MTS by amplitude demodulation. A carrier signalTS extracted by the clock extraction stage 8 can be applied to thedemodulation means 9 for this purpose. An encoded data signal DS1contained in a received modulated carrier signal MTS can be output bythe demodulation means 9.

The smart card 1 includes decoding means 10 which are arranged to decodean encoded data signal DS1 output by the demodulation means 9 and tooutput data D contained in the encoded data signal DS1.

The smart card 1 also includes data processing means 11 which arearranged to process the data output by the decoding means 10. To thisend, the data processing means 11 include a microprocessor (not shown inFIG. 1) and storage means (not shown in FIG. 1). The storage means ofthe data processing means 11 store the previously mentioned balance dataof the amount due to the user of the smart card 1. The data processingmeans 11 can be supplied with the carrier signal TS extracted by theclock extraction stage 8 in order to process data.

The decoding means 10 of the smart card 1 include a first decoding stage12 and a second decoding stage 13, the first decoding stage 12 beingarranged to decode a data signal DS1(RTZ) encoded in conformity with thereturn-to-zero encoding method whereas the second decoding stage 13 isarranged to decode a data signal DS1(MI) encoded in conformity with theMiller encoding method.

This offers the advantage that the decoding means 10 of the smart card 1are arranged to decode a received encoded data signal DS1 which has beenencoded in conformity with the Return-To-Zero encoding method in thebase station 2 or in conformity with the Miller encoding method in afurther base station. As a result, the smart card 1 can be used in aplurality of fields of application, for example for access controlsystems or toll systems, in which the Return-To-Zero code or the Millercode are customarily used or even standardized. It is thusadvantageously possible to realize data carriers of the type A and thetype B in conformity with an “Approximity Standard” (ISO 14 443) in thesmart card 1.

The first decoding stage 12 and the second decoding stage 13 can besupplied with an encoded data signal DS1 which is output by thedemodulation means 9 and contains the transmission data ÜD to betransmitted to the smart card 1 by the base station 2. The firstdecoding stage 12 is arranged to output first data D1 after completionof the decoding operation in the first decoding stage 12. The seconddecoding stage 13 is arranged to output second data D2 after completionof the decoding operation in the second decoding stage 13.

It is to be noted that there are various factors which could influencethe transmission of transmission data ÜD from a base station to thesmart card 1; such factors could be the cause that data output by thedecoding means 10 of the smart card 1 do not correspond to thetransmission data ÜD transmitted by the base station. One such factoroccurs when the encoding means of a base station encode transmissiondata ÜD in conformity with one encoding method and the decoding means 10of the smart card 1 decode the received encoded data signal DS1 inconformity with a different encoding method. Another factor consists inthe superposition of a noise signal on the modulated carrier signal MTSduring the transmission in the electromagnetic alternating field; such anoise signal introduces errors in the data output by the decoding means10 during the demodulation by means of the demodulation means 9 and/orduring the decoding by means of the decoding means 10.

The first decoding stage 12 evaluates the redundancy data RD containedin the first data D1 in order to check whether the received first dataD1 correspond to the transmission data ÜD transmitted by the basestation 2. The evaluation of the redundancy data RD contained in thefirst data D1 is performed in conformity with the generating of theredundancy data RD in the base station 2. To this end, the firstdecoding stage 12 calculates the sum of digits of the bit sequencecontained in the first data D1 and corresponding to the debit data AD.The result of this calculation is compared with the redundancy data RDcontained in the first data D1.

If this comparison yields correspondence, it may be assumed that thefirst data D1 determined by the first decoding stage 12 correspond tothe transmission data ÜD transmitted to the smart card 1 by the basestation 2. In this case positive first decision supporting informationEUI1 can be output by the first decoding means 12. Decision supportinginformation EUI supports a decision operation during which it is decidedwhether the decoding means 10 should output the first data D1 or thesecond data D2 to the data processing means 11 for further processing.

However, if the described comparison does not reveal correspondence, itmust be assumed that the first data D1 determined by the first decodingstage 12 do not correspond to the transmission data ÜD applied to thesmart card 1 by the base station 2. In this case the first decodingmeans 12 output negative first decision supporting information EUI1.

The second decoding stage 13 is capable of delivering second decisionsupporting information EUI2 which is determined in the same way as thefirst decision supporting information EUI1, be it that debit data AD andredundancy data RD contained in the second data D2 is then evaluated.

The decoding means 10 of the smart card 11 include a decision stage 14which is arranged so as to decide which of the decoding stages 12 or 13is suitable to decode a received encoded data signal DS1. To this end,the first decision supporting information EUI1, determined by the firstdecoding stage 12, and the second decision supporting information EUI2,determined by the second decoding stage 13, can be applied to thedecision stage 14.

The decision stage 14 is arranged to decide, by evaluation of thereceived decision supporting information EUI1 and EUI2, which of thedecoding stages 12 or 13 is suitable to decode the received encoded datasignal DS1. The decision stage 14 decides that the first decoding stage12 is suitable to decode the received encoded data signal DS1 if itreceives positive first decision supporting information EUI1.Analogously, the decision stage 14 decides that the second decodingstage 13 is suitable to decode the received encoded data signal DS1 ifit receives positive second decision supporting information EUI2. Incase positive decision supporting information EUI1 and EUI2 or negativedecision supporting information EUI1 and EUI2 is output by the firstdecoding stage 12 as well as by the second decoding stage 13, thedecision stage 14 is arranged to carry out further checks so as todecide which of the decoding stages 12 or 13 is suitable to decode thereceived encoded data signal DS1. For example, in such a case the smartcard 1 can transmit request information to the base station 2; inresponse thereto the base station 2 transmits the previously transmittedtransmission data ÜD again.

The decision stage 14 can apply decision information EI to the dataprocessing means 11, which decision information characterizes thedecoding stage 12 or 13 which is suitable to decode the received encodeddata signal DS1. The data processing means 11 are arranged to processthe first data D1 or the second data D2, depending on the decisioninformation EI applied thereto.

The decoding means 10 of the smart card 1 also include a storage stage15 in which the first data D1, output by the first decoding stage 12,and the second data D2, output by the second decoding stage 13, can bestored. The data processing means 11 are connected to the storage stage15 in order to enable the reading out of first data D1 or the seconddata D2 after the appearance of decision information EI from thedecision stage 14.

Including the storage stage 15 in the smart card 1 offers the advantagethat data D1 and D2 output by the decoding stages 12 and 13 is firstbuffered and can be read out from the storage stage 15 by the dataprocessing means 11 after the arrival of decision information EI fromthe decision stage 14. Thus, data D1 and D2 received and decoded beforethe arrival of decision information EI will not be lost.

The operation of the smart card 1 upon reception of a modulated carriersignal MTS will be described in detail hereinafter on the basis of afirst example. According to this first example, the base station 2transmits the modulated carrier signal MTS which is shown in FIG. 8 andcontains the data signal DS1(RTZ) which has been encoded in conformitywith the Return-To-Zero encoding method and contains the bit sequence“10010” of the transmission data ÜD.

The modulated carrier signal MTS is received by the transmission andreceiving means 5 so as to be applied to the demodulation means 9. Thedemodulation means 9 perform amplitude demodulation of the modulatedcarrier signal MTS shown in FIG. 8.

FIG. 9 shows a waveform of the encoded data signal DS1 output by thedemodulation means 9. Because at this time the smart card 1 does nothave information available as regards the encoding method used to encodethe encoded data signal DS1 output by the demodulation means 9, theencoded data signal DS1 is applied to the first decoding stage 12 and tothe second decoding stage 13.

In the first decoding stage 12 the encoded data signal DS1 appliedthereto is decoded in conformity with the Return-To-Zero method and thebit sequence “100110” shown in FIG. 9 is determined as the first dataD1. The first data D1 is applied to the storage stage 15 so as to bestored.

From the first data D1 the first decoding means 12 then determine thebit sequence “1001” which corresponds, on the basis of its position inthe bit sequence “100110” of the first data D1, to the bit sequence ofthe debit data AD. In order to check whether this debit data ADcorresponds to the debit data AD transmitted by the base station 2, thefirst decoding means 12 calculate the sum of the bit sequence “1001”with the value “2”. This value “2”, being the sum of the debit data ADcontained in the first data D1, is then compared with the reference dataRD with the bit sequence “10” contained in the first data D1; thisreference data also has the value “2”. Because the value of the sum ofthe debit data AD corresponds to the value of the reference data RD ofthe first data D1, the first decoding stage 12 applies positive firstdecision supporting information EUI1 to the decision stage 14.

In the second decoding stage 13 the encoded data signal DS1 appliedthereto is decoded in conformity with the Miller method. According tothe Miller method, in the case of two successive bits “0” in a bitsequence a time interval TB is awaited (as shown in FIG. 4) during whichthe encoded data signal DS1(MI) has a low amplitude value; therefore,the second decoding stage 13 cannot decode the third bit, so that a “?”is inserted in the bit sequence “10?110” of the second data D2 shown inFIG. 9. The second data D2 shown applied to the storage stage 15 so asto be stored.

From the second data D2 the second decoding means 12 then determine thebit sequence “10?1” which corresponds, on the basis of its position inthe bit sequence “10?110” of the second data D2, to the bit sequence ofthe debit data AD. Because one bit of the debit data AD could not bereliably decoded, the second decoding means 13 output negative seconddecision supporting information EUI2 to the decision stage 14.

On the basis of the received positive first decision supportinginformation EUI1 and the negative second decision supporting informationEUI2, the decision stage 14 then applies decision information EI whichcharacterizes the first decoding stage 12 to the data processing means11.

In response thereto the data processing means 11 read out the first dataD1 stored in the storage stage 15 and determine the debit data ADcontained in the first data D1 with the bit sequence “100” correspondingto the value “9”. The data processing means 11 then subtract the value“9” of the debit data AD from the balance data stored in the dataprocessing means 11 and store the calculated value as balance data againin the data processing means 11, so that the fare amounting to “9” euroshas been debited to the account balance of the user of the smart card 1.

This offers the advantage that transmission data ÜD encoded by the basestation 2 in conformity with the Return-To-Zero method as well astransmission data ÜD encoded in conformity with the Miller method by afurther base station can be decoded by the decoding means 10 of thesmart card 1 and hence can be processed by the smart card 1. Therefore,the smart card 1 can be used for a variety of fields of application.

The operation of the smart card 1 upon reception of a modulated carriersignal MTS will now be described in detail on the basis of a secondexample. The smart card 1 is also arranged to receive a modulatedcarrier signal MTS containing an encoded data signal DS1 which includesdecoding stage instruction information BI. Decoding stage instructioninformation BI may in such case be formed by a special bit sequence, forexample “1111”, of the debit data AD. This debit data AD, having the bitsequence “1111”, can be transmitted to the smart card 1 by the basestation 2 in conformity with the previously described first example, andis ultimately read out from the storage stage 15 by the data processingmeans 11 for the further processing of the debit data AD.

The data processing means 11 are arranged to output, in response to theappearance of the bit sequence “1111” as the debit data AD, decodingstage instruction information BI to the decision stage 14. The decisionstage 14 is arranged to decide, by evaluation of the decoding stageinstruction information BI applied thereto, which of the decoding stages12 or 13 is intended to decode a next encoded data signal DS1 that canbe received. The decision stage 14 can supply the data processing means11 with appropriate decision information EI.

This offers the advantage that the base station 2 can supply the smartcard 1 with decoding stage instruction information BI which is containedin the modulated carrier signal MTS and is capable of characterizing thedecoding stage 12 or 13 intended to decode an encoded data signal DS1transmitted in the modulated carrier signal MTS by the base station 2after the transmission of the decoding stage instruction information BI.The base station 2 can thus select for the smart card 1 the decodingstage 12 or 13 of the smart card 1 which will be suitable for decodingthe encoded data signal DS1.

The smart card 1 includes encoding means 16 for supplying an encodeddata signal DS2, which encoding means include a first encoding stage 17and a second encoding stage 18. In the transmission mode of the smartcard 1, the data processing means 11 can supply the base station withthird data D3 to be transmitted, i.e. to the first encoding stage 17 orto the second encoding stage 18. The first encoding stage 17 is arrangedto encode third data D3 applied thereto in conformity with the frequencykeying encoding method and to output an encoded data signal DS2. Thesecond encoding stage 18 is arranged to encode third data D3 appliedthereto in conformity with the phase keying encoding method and tooutput an encoded data signal DS2 which contains the third data D3.

The smart card 1 also includes modulation means 19 which are arranged tomodulate the encoded data signal DS2 output by the encoding means 16 andto output a modulated carrier signal MTS. The modulation means 19 arearranged to modulate the encoded data signal DS2 applied thereto by wayof load modulation as has since long been known.

A modulated carrier signal MTS output by the modulation means 19 can beapplied to the terminal 6 of the transmission and receiving means 5 ofthe smart card 1 and transmitted to the base station 2 or to a furtherbase station which is not shown in FIG. 1.

This offers the advantage that the smart card 1 is also suitable fortransmitting an encoded data signal DS2 which is contained in amodulated carrier signal MTS and contains third data D3 which has beenencoded in conformity with the frequency keying method or the phasekeying method. As a result, the smart card 1 can be used in a pluralityof fields of application in which communication with a base station ispossible while utilizing only one of the said codes.

FIG. 10 shows a block diagram of a base station 2 and a smart card 1which constitutes a second embodiment of a data carrier according to theinvention. The second embodiment of the smart card 1 according to theinvention corresponds to the first embodiment of the smart card 1according to the invention; stages of decoding means 20 of the secondembodiment correspond to stages of the decoding means 10 of the firstembodiment. The decoding means 20, however, include a storage stage 15in which a received encoded data signal DS1 can be stored prior to thedecoding by the first decoding stage 12 and the second decoding stage13.

This offers the advantage that data received by the smart card 1 beforea decision has been taken as to which decoding stage 12 or 13 issuitable for decoding a received encoded data signal DS1 will not belost.

It is to be noted that a data carrier according to the invention neednot necessarily be provided with storage means for storing a receivedencoded data signal or for storing data output by the decoding stages.However, it has been found that it is advantageous when in such a datacarrier data D1 output by the first decoding stage are applied to thedata processing means for further processing before the decision stagecan decide which of the decoding stages is suitable for decoding areceived encoded data signal DS1.

When the first decoding stage is then arranged to decode an encoded datasignal in conformity with a method customarily used for the encoding oftransmission data ÜD by a base station, data of an encoded data signalDS1 received prior to the arrival of decision information EI from thedecision stage are usually already correctly decoded; this constitutes amajor advantage.

It is to be noted that decoding means of a data carrier according to theinvention may also include three, five, ten or even more decodingstages, each of which decodes a received encoded data signal inconformity with a respective different method. This offers the advantagethat data signals encoded in conformity with a plurality of differentcodes can be decoded in the data carrier and that the data contained inthe encoded data signals can be processed.

Furthermore, it is to be noted that encoding means of a data carrieraccording to the invention may also include three, five, ten or evenmore encoding stages for encoding third data to be transmitted to a basestation in conformity with a plurality of different encoding methods.The respective coding stage used can then be defined by the dataprocessing means of the data carrier according to the invention but alsoby the base station, communicating with the data carrier, bytransmission of encoding stage instruction information.

It is to be noted that demodulation means of a data carrier according tothe invention may also include several demodulation stages which arearranged to demodulate modulated carrier signals which have beenmodulated by amplitude modulation with different modulation depths. Thisoffers the advantage that amplitude modulated carrier signals withmodulation depths of, for example, 10%, 20%, 50% or 70% can also bedemodulated.

It is also to be noted that a decoding stage can output negativedecision supporting information EUI, for example, also if the error rateof the data determined in the decoding stage exceeds a given error ratethreshold.

It is also to be noted that the inclusion of at least two decodingstages is also advantageous in a data carrier which is arranged todemodulate a received modulated carrier signal which has been modulatedby frequency modulation or phase modulation.

Finally, it is to be noted that if a data signal DS1(PSK), as is shownin FIG. 7, encoded in conformity with the phase keying code, would bedecoded by a decoding stage which decodes encoded data signals DS1 inconformity with the frequency keying code, the output for all bits ofthe transmission data were bits “1” or bits “0”. For this case thedecision stage is arranged to decide, by checking the reference datacontained in the transmission data, which of the decoding stages issuitable for decoding the encoded data signal.

1. A data carrier comprising: receiving means for receiving a modulatedcarrier signal which contains an encoded data signal encoded inconformity with an encoding method, and said encoded data signalincluding decoding instruction information; demodulation means fordemodulating the received modulated carrier signal and for outputtingthe encoded data signal contained therein, decoding means for decodingthe encoded data signal and for outputting data, and data processingmeans for processing the data output by the decoding means,characterized in that the decoding means including at least a firstphysical decoding stage and a second physical decoding stage, the firstdecoding stage being arranged to decode said data signal encoded inconformity with a first decoding method whereas the second decodingstage is arranged to decode a data signal encoded in conformity with asecond decoding method and wherein said first decoding method isManchester and the second decoding method is Miller; and wherein saiddecoding means further includes a decision stage capable of determiningwhich of the first and second stages decodes the encoded data signal. 2.(canceled)
 3. (canceled)
 4. A data carrier as claimed in claim 2,wherein the decoding stage instruction information includes redundancydata.
 5. A data carrier as claimed in claim 1, wherein the decodingmeans includes a storage stage in which the encoded data signal can bestored prior to being read out by the data processing means. 6.(canceled)
 7. A data carrier as claimed in claim 1, further comprisingan encoding means for outputting an encoded data signal, said encodingmeans including at least a first encoding stage and a second encoding.8. A data carrier as claimed in claim 7, wherein said first encodingstage is designed to encode data in conformity with a third method andsaid second encoding stage is designed to encode data in conformity witha fourth method which is different from said third method.
 9. A datacarrier as claimed in claim 1, further comprising modulation meansdesigned to modulate the encoded data signal output.
 10. A data carriercomprising: a receiver designed to receive a modulated carrier signalwhich includes an encoded data signal; demodulator capable of receivingthe modulated carrier signal and designed to output the encoded datasignal included therein; decoder designed to decode the encoded datasignal and to output data; data processor designed to process the outputdata from the decoder; and wherein the decoder includes a first decodingstage and a second decoding stage, the first decoding stage designed todecode the encoded data signal which is encoded in conformity with afirst encoding method and the second decoding stage designed to decodethe encoded data signal encoded in conformity with a second encodingmethod, wherein said first encoding method is No-Return-To-Zero (NRZ)and second encoding method is Miller and wherein both the first decodingstage and the second decoding stage attempt to decode the encoded datasignal.
 11. The data carrier of claim 10, wherein the data is output tothe data processor before a decision stage determines which of the firstand second decoding stages is suitable for decoding the encoded datasignal.
 12. A method comprising: receiving a modulated carrier signalhaving an encoded data signal; demodulating the modulated carrier signalin a demodulator and outputting the encoded data signal containedtherein to a decoder; decoding the encoded data signal and outputtingdata to a data processor; processing the data output by the decoder;wherein the decoding step includes a first decoding stage which decodesthe encoded data signal in conformity with a first decoding method and asecond decoding stage which decodes the encoded data signal inconformity with a second decoding method, wherein the first decodingmethod is Manchester and the second decoding method is Miller; andwherein the decoding step further includes a decision stage whichdetermines which of the first and second decoding stages decodes theencoded data signal.
 13. The method of claim 14, wherein the data isoutput by the first decoding stage to the data processor before thedecision stage decides which of the first and second decoding stages issuitable for the decoding of the encoded data signal.
 14. The method ofclaim 14, wherein the decision stage evaluates decision supportinginformation to determine which of the first and second decoding stagesis suitable to decode the encoded data signal.
 15. The method of claim14, wherein the decoding step further includes a storage stage in whichthe encoded data signal may be stored prior to the decoding by the firstand second decoding stages.
 16. The method of claim 14, furthercomprising: a first encoding stage which encodes data in conformity witha third decoding method; and a second encoding stage which encodes datain conformity with a fourth decoding method.
 17. The method of claim 19,wherein the third encoding method is frequency shift keying (FSK) andthe fourth encoding method is phase shift keying (PSK).
 18. A datacarrier comprising: receiving means for receiving a modulated carriersignal which contains an encoded data signal, demodulation means fordemodulating the received modulated carrier signal and for outputtingthe encoded data signal contained therein, decoding means for decodingthe encoded data signal and for outputting a data signal, dataprocessing means for processing the data signal output by the decodingmeans, the decoding means including at least a first decoding stage anda second decoding stage, the first decoding stage being arranged todecode said data signal in conformity with a first decoding method whilesimultaneously the second decoding stage is arranged to decode said datasignal in conformity with a second decoding method, and a decision stagewhich is arranged to decide which of the first and second decodingstages is suitable to decode said data signal.
 22. A data carriercomprising: receiving means for receiving a modulated carrier signalwhich contains an encoded data signal, demodulation means fordemodulating the received modulated carrier signal and for outputtingthe encoded data signal contained therein, decoding means for decodingthe encoded data signal and for outputting data, data processing meansfor processing the data signal output by the decoding means, thedecoding means including at least a first physical decoding stage and asecond physical decoding stage, the first decoding stage being arrangedto decode said data signal in conformity with a first decoding methodwhile in parallel the second decoding stage is arranged to decode saiddata signal in conformity with a second decoding method, and a decisionstage which is arranged to decide which of the first and second decodingstages decodes said data signal.
 23. A data carrier comprising:receiving means for receiving a modulated carrier signal which containsan encoded data signal, demodulation means for demodulating the receivedmodulated carrier signal and for outputting the encoded data signalcontained therein, decoding means for decoding the encoded data signaland for outputting data, data processing means for processing the dataoutput by the decoding means, the decoding means including at least afirst decoding stage and a second decoding stage, the first decodingstage being arranged to decode said data signal in conformity with afirst decoding method while simultaneously the second decoding stage isarranged to decode said data signal in conformity with a second decodingmethod, wherein said first decoding method is Manchester and said seconddecoding method is Miller; and a decision stage which is arranged todecide which of the first and second decoding stages decodes said datasignal.
 24. A data carrier comprising: receiving device capable ofreceiving a modulated carrier signal which contains an encoded datasignal, demodulation device configured to demodulate the receivedmodulated carrier signal and outputs the encoded data signal containedtherein, decoding device capable of decoding the encoded data signal andoutputting data, said decoding device including at least a firstdecoding stage and a second decoding stage, the first decoding stage isarranged to decode said data signal in conformity with a first decodingmethod whereas the second decoding stage is arranged to decode said datasignal in conformity with a second decoding method, a decision stagewhich determines which of the first and second decoding stages issuitable to decode the encoded data signal, and data processing deviceconfigured to process the data output by the decoding device, whereinonce the decision stage applies decision information to the dataprocessing device regarding which of the first and second decodingstages decodes the encoded data signal, the determined first or seconddecoding stage is used for processing the remainder of the encoded datasignal.
 25. The data carrier of claim 24, wherein the first decodingmethod is Manchester and the second decoding method is Miller.
 26. Adata carrier as claimed in claim 10, wherein said encoded data signalhas a structure that ensures that time intervals with high amplitudevalue of the modulated carrier signal are substantially at least as longas time intervals with low amplitude value of the modulated carriersignal.